Gliederung

All modern cochlear implant systems allow to record the response of the auditory nerve. This technique is currently a part of the clinical routine. However, the proper method of artefact reduction is still under discussion. After the electrical stimulus some residual charge remains on the contacts and in the tissue close to the contacts that drives the amplifier into saturation. In addition, residual charge decays with a similar time scale as neural response waveforms, resulting in artefact that can distort the measured neural signal. SchlÃ¶sser, Zierhofer and Hochmair [Ref.Â 1] showed that it is possible to reduce the residual charge by introducing a third phase to the stimulus. The artefact could be significantly reduced. The research software "Bionic Ear Data Collection System" for the Advanced Bionics implants CII and HiRes90K allows to record the neural response imaging (NRI) with flexible stimulation patterns. It was used within a study to compare artefact reduction via alternating stimulus polarity with reduction via a third phase in a group of 10 post-lingual deaf adults. Responses were recorded at sub-threshold and supra-threshold levels as a function of amplitude of the third phase relative to the two initial phases. We also assessed whether loudness evoked by triphasic pulses was similar to that evoked by biphasic pulses of similar amplitude for the first two phases by performing a loudness-balancing task between the two stimuli. Preliminary data indicate that optimal third phase reduces the stimulus artifact. Thus, the first negative peak, N1, is less distorted and latency as well as amplitude can be defined more reliably.